Skeletal deformities become evident during the growth of an individual or may be acquired from events such as trauma, tumor resection, or systemic disease.
Correction of bone deformities may require surgical treatment to reposition the deformed bones into a "normal" relationship or by orthopedically guided bone movements. Currently, pins or other transosseous devices are used in conjunction with some surgical procedures to anchor or move the bones and to maintain bone position during treatment and healing. These transosseous devices penetrating into the medullary bone have limitations in some regions of the human skeleton. In the jaw bone, there are tooth roots and developing tooth buds in the juvenile which may prevent pins from being used. The correction of facial deformities presents clinical challenges which have led to this invention. In other areas, such as the skull, the bone is too thin to stabilize a transosseous device. If or when pressure is applied, the pins will dislodge and preclude correction of the cranial deformity.
Often, the earliest signs of maxillary (upper jaw) or mandibular (lower jaw) growth disharmony is dental malalignment. Once recognized, it is possible to guide the growth of the segments of the cranio-facial skeleton to minimize the need for surgical correction of the deformity. Maxillary hypoplasia (deficiency) exists in all three dimensions. Transverse deficiency of the maxilla is commonly treated by orthodontists with orthopedic palatal expansion. Morphologically, this is possible due to the existence of a patent mid-palatal suture. Deficiency in the maxilla in the vertical or anterior-posterior (A-P) direction has not been satisfactorily performed by orthopedically guided movements because a lack of an existent transverse suture line. Orthodontists employ orthopedic traction primarily in the A-P dimension to control or direct the development of the mandibular jaw bone to a favorable position. Mandibular deficiency can be corrected by functional appliances which position the mandible forward and presumably allow for a posterior condylar appositional growth which stabilizes the mandible in this forward position.
Cleft palate patients often have transverse, anterior-posterior, and vertical dysplasia of the maxilla. Treatment of these patients often involves orthodontic alignment of the alveolar (tooth bearing) segments prior to bone grafting the alveolar defects. However, the defects can be large and difficult to manage when the patient is young. The deciduous dentition can also be difficult to manage since there is inadequate orthodontic anchorage. This can prevent definitive alignment of the arches until the patient is in the early teens.
All orthodontic and orthopedic forces adhere to Newton's "Law of Reciprocal Forces." If a force is applied to retract or pull back an object such as a tooth, there exists an "equal and opposite" force to move another tooth or object forward. The resistive value of the teeth is known as anchorage. Orthodontists may offset these reciprocal tendencies by using an extraoral force known as a headgear to augment the resistive value of the teeth.
However, patient compliance is often inadequate. Many patients do not want to wear the headgear, compromising orthodontic therapy and often the final result. Orthodontic forces are usually continuous, acting 24 hours a day. Realistically, most patients will not wear headgear more than 10-12 hours/day. Therefore, the posterior anchorage is typically fortified 40-50% of the time. All too often, inconsistent usage or overt noncompliance will reduce this effect even more. The trans-palatal arch wire or bar by itself will cause reciprocal forces between the teeth to which the wire is attached. It will not implant special properties to these teeth beyond the simple additive values of the same two teeth. Both orthodontists and their patients will welcome a device which is simple to install, obviates the necessity to wear extraoral devices, helps to decrease the total time, and permits a more predictable result.
Previous work in this field indicates that endosseous implants can be used to anchor orthodontic forces for tooth movement. These studies indicate that osseointegrated implants have been used to anchor realignment of the teeth without reciprocal movement by the implants. All of these implants were placed deeply into the bone.
Endosseous implants are not suitable in juvenile or adolescents for two reasons. First and foremost, endosseous implants are inserted into a hole which is drilled into the alveolar (tooth bearing) portion of the jawbone. Insertion of an endosseous implant into these areas will harm unerupted teeth which are forming in these areas. Since the juvenile and adolescent patients are still growing, an endosseous implant will be engulfed with continuing vertical development of the alveolar bone and would progressively sink to a lower level to the point that it becomes inaccessible, not useful, and inherently difficult to remove.
In juveniles or adolescents with skull deformity the neurosurgeon or plastic surgeon is often faced with a very difficult, high-risk surgery to incise the skull and abruptly reposition the cranial bones. This almost always involves communication with the brain cavity and carries with it the grave risks associated with such procedures. Transosseous pins to anchor expansion devices in the cranium are contraindicated because they would penetrate into the dura or sinusoids, or because of the thinness of the cranium, the pins would dislodge and fail to anchor the required bone movements. The use of transosseous pins in small bones such as the hands is precluded because of the size limitation of the pins being larger than the medullary cavity of the intended bones.
In orthopedic surgery it is sometimes necessary to attach devices to a bone. In the case of trauma, this may be necessary to stabilize the fragments while healing occurs. In other cases, it is desirable to apply fores to a bone which is deficient in size or misshapen. There is a technique called distraction osteogenesis (DO) which allows a bone to be stretched with an expansion device after the cortical surface has been incised.
To stabilize these devices, threaded pins are inserted deeply into the bone. These pins are known as transosseous pins. They work well in long bones but there exists a need to attach devices to thin bones such as the skull or mandible. This subperiosteal bone anchor has been successfully tested in this regard and will allow surgeons to attach devices to small or thin bones using surface adherent technology.
The objectives of this invention can be stated as follows.
1. It must not deeply enter the bone, but should attach to the cortical surface. PA1 2. It should be thin to lay under the soft tissue against the bone without creating significant inflammation or bulk. PA1 3. It should have versatility of attachments in order to assume a role for an orthodontic anchor, an orthopedic anchor, or attach other devices to a bone such as a pacemaker, hearing aid, prosthesis, insulin pump, or other medical or dental devices. PA1 4. It must have sufficient shear strength, to resist forces placed upon it from orthodontic or orthopedic devices or to stabilize devices that may be attached to it.